Risks To Consider When Changing Your Corn-Soybean Rotation

Are you weighing a change in crop rotation for 2019? Some growers, in anticipation that the tariffs with China will be finally resolved, are planning to go with beans-on-beans. Still others have the opposite mindset and are considering planting corn-on-corn.

Based on Field Agronomist Ken Ferrie’s 2018 field plots, he says you’ll potentially take a 5-bushel to 6-bushel per acre yield hit when you grow beans-on-beans versus yield results in a beans-after-corn rotation.

“That was the case in our beans-on-beans plot this past year. Our early April planted beans on beans yielded 80 bu. on average compared to the 86-bu. [in the rotated plot],” says Ferrie, Farm Journal Field Agronomist and owner of Crop-Tech, Inc., based in central Illinois.

Ferrie says he isn’t 100% sure why the yield lag exists but suspects it is due to disease or insect pressure, or some combination of the two. With that said, the 2018 season was a good year for fungicide-insecticide applications.

“We saw a 0- to 8-bushel response range to applications in soybeans with a lot in the 3- to 5-bushel range,” he notes. “Early-planted April soybeans gave a stronger response to the applications than later-planted beans.” He adds that tillage practices made little to no difference in response.

For farmers who grew beans-on-beans and are going back to corn in those fields in 2019, Ferrie says they are likely to see less disease in those fields. “That should help lower corn nematode populations but may not help with first-year corn rootworm issues,” he notes.

Ferrie says if farmers documented a lot of rootworm beetle in their bean fields this year or saw a lot of beetles on the windshield of their combine at harvest, they’ll need to protect their 2019 corn crop from rootworm.

“Eliminating a fungicide from your program next year may not be feasible then,” he says.

Farmers who are rotating bean-on-bean fields back to corn next year often ask Ferrie if they will get a double-nitrogen credit and be able to reduce their nitrogen use. He says the short answer is no.

“Set your nitrogen rate for first-year corn, and then back it up with in-season nitrate testing at sidedressing time,” Ferrie advises. “If the testing says you can pull back on your nitrogen at that point, then do it but don’t budget to do that now.”

If you decide to go with corn again in the same fields next year, Ferrie says to anticipate getting a 10% to 15% reduction in yield. “Make sure you account for the carbon penalty, disease and insects as well, and that might minimize the hit you take,” he says. “But if Mother Nature turns things dry long enough in the season, corn-on-corn will suffer and there’s not much you can do about it.”